1. Field of the Invention
The present invention relates to an electrostatic actuator suitable for use in, for example, driving a movable member, which is disposed at a substrate, by electrostatic forces generated between electrodes.
2. Description of the Related Art
In general, various types of very small actuators can be formed at, for example, a silicon substrate by, for example, micromachining. Of the various types of very small actuators, the type that uses electrostatic forces can be easily processed in addition to easily providing drive forces even when it is small, so that this type of actuator is widely used as an electrostatic actuator.
An electrostatic actuator which is manufactured using a first related technology is known to have a structure in which, for example, a flat electrode is formed above a substrate with a gap therebetween and is displaced in a direction that is perpendicular to the substrate by applying a voltage to the electrode.
An electrostatic actuator which is manufactured using a second related technology has a structure in which two comb-shaped electrodes, a movable electrode and a stationary electrode, are engaged, and the movable electrode is displaced with respect to the stationary electrode in the direction of extension of the electrode fingers by applying a voltage between the electrodes.
An electrostatic actuator which is manufactured using a third related technology has a structure which is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 5-21976, in which a plurality of electrodes are connected and arranged in the form of an accordion, and the electrodes arranged in the form of an accordion are displaced by being extended and contracted by applying a voltage between a stationary electrode and the electrodes arranged in the form of an accordion.
In the first related technology, since a sufficient electrostatic force is provided by providing the gap between the flat electrode and the substrate small, the amount of displacement of the electrode is limited to a small value due to the size of the gap, so that it becomes difficult to realize an actuator which needs to be greatly displaced. Thus, the scope of application and number of applications are limited.
In the second related technology, the gap between the two electrodes that engage each other is limited by, for example, the processing precision, so that it is difficult to generate a large electrostatic force between the electrodes. Therefore, in order to easily displace the movable electrode even by a small electrostatic force, it is necessary to set, for example, the spring constant of a beam supporting the movable electrode to have a small value. Therefore, the rigidity of a movable member including the electrode tends to be small, so that it is difficult to realize an actuator which has a required, sufficiently high rigidity.
In the third related technology, since the electrodes arranged in the form of an accordion extend and contract as a whole, there is a limit as to how large the rigidity of the electrodes can be, so that this technology has the same problem as the second related technology. In addition, since individual members which are bent in the form of an accordion extend and contract, respectively, it is difficult to achieve a suitable amount of displacement for the electrodes as a whole.